1. Field of the Invention
This invention relates to the field of local computer networks and finds particular application when used with a high speed digital serial bus such as a coaxial cable. The specifications for a typical high speed digital serial link have been proposed and are known as the Ethernet. The Ethernet has been adopted as IEEE 802.3 Local Area Network Standard.
The present application is an improvement in the interface between the computer and the coaxial cable. One such interface has been described in the co-pending parent application Ser. No. 242,708, the subject matter of which is incorporated herein by reference and made a part hereof.
2. Description of the Prior Art
The parent application addresses and cites many of the references associated with the Ethernet local area communication system. In addition, U.S. Pat. No. 4,254,496, issued to Munter describes a digital communication system in which a local modem adapter employs transmit and receive lines and a line control circuit. The Munter reference fails to teach or show a collision detect channel and associated circuitry. U.S. Pat. No. 2,852,760 to Eckhardt describes a coded carrier remote control system employing balanced circuitry in which transformers are coupled directly to a communication medium. All stations transmit at the same frequency under a continuously transmitted pilot frequency generated at a control station. By contrast, in the present systems, there is no control station or slave stations. The Ethernet standard calls for a very high impedance coupling as compared with other media, which imposes a different set of constraints than is imposed upon other systems.
As the Ethernet standard local area network becomes more accepted, there has developed a need for more reliable, compact and efficient interface between the computer and the medium. In particular, there is a need to eliminate DC to DC converter apparatus used to power circuitry on the coaxial medium side of the medium isolation transformers.